Dana Nieder was at a loss. Doctors had been trying to figure out what was wrong with her daughter Maya since she was 7 months old. Now 4 1/2, Maya didn’t learn to walk until long after her second birthday and still can say only a few words. After exhausting other possibilities, Nieder decided to have part of Maya’s genome sequenced in a test so new that health insurers have balked at paying for it. “It seemed to be our only chance to find a genetic answer,” says Nieder, a former middle school science teacher from New York City.

Unlocking the secrets of human DNA is one of the most promising avenues of medical research. (Read TIME’s complete series on genetic testing and families.) But along with a host of scientific and ethical issues, genome sequencing raises some tough economic questions at a time when U.S. health care costs are already spiraling. How much is this going to cost, and who’s going to pay?

The final chapter in a five-part series exploring the promise and pitfalls of sequencing children’s genomes

Whole-genome sequencing (WGS) is already relatively inexpensive — labs can analyze a person’s entire genetic code for under $10,000 — and the cost is dropping fast. But for some patients, this initial DNA report is the beginning, not the end, of their medical odyssey. And whether those journeys will increase the nation’s health costs isn’t clear.

In an ideal scenario, genetic analysis could save money by catching diseases early, offering targeted treatments and underscoring the most effective preventive measures. In the worst case, it could deluge an already swamped health care system, as patients with ambiguous results begin to seek frequent screenings — and potentially unnecessary procedures — for diseases they might never develop. Princeton health care economist Uwe Reinhardt sees a future that skews toward the latter: “If someone held a gun to my head, I would have to say it will cost a lot more and it will create an enormous amount of anxiety. A certain amount of ignorance is really bliss.”

More than half of the 1,254 doctors surveyed this year by UnitedHealthcare said they think new genetic tests will increase overall health care spending; just 1 in 5 think the tests will lower costs. One of the country’s largest insurers, UnitedHealthcare estimates the U.S. spent more than $5 billion on genetic testing in 2010. By 2021, the company says, total spending on genetic testing could rise to $25 billion, a figure based in part on its prediction that WGS will become widely available soon.

For now, scanning a patient’s entire genome is cutting-edge technology, and health insurers rarely cover it. The reason, industry officials say, isn’t the cost; they note that insurers already cover hundreds of expensive tests targeting specific genes. Rather, the insurers say they’re cautious because the technology is new and unproved; they also share the CDC’s concern that geneticists don’t yet know how to interpret all the results.

Slight differences, or variants, in people’s genetic code are what make us unique. Some of these differences are known to increase the risk of disease; others don’t seem to matter. “Everyone has in the neighborhood of 3 million variants,” says Dr. Joanne Armstrong, senior medical director of Aetna. “Of those variants, there’s a significant chunk where we’re not sure what they mean. So it’s kind of noise vs. signal.”

Consider full-body MRIs, for example, which have been shown to generate false positives that lead to unnecessary tests. The same would be true if sequencing is used indiscriminately, says Dr. Jim Evans, a professor of genetics and medicine at the University of North Carolina at Chapel Hill and the editor-in-chief of Genetics in Medicine. “Ninety-eight percent of us have very boring genomes,” he says. “Most diseases have a genetic component, but your genomic information provides precious little in the way of tangible guidance for you to live a healthy life. You don’t need to sequence someone’s genome to tell them they should be exercising and eating right.”

Yet studies indicate that most people want tests that can predict their risk of future disease, even if learning about those risks offers no leg up on treatment. A study published in 2010 in Health Economics found that up to 88% of people said they would like to take a test that could foretell their odds of developing arthritis, Alzheimer’s and other diseases.

What those survey respondents probably didn’t know is that getting those test results could make it hard for them to buy life insurance, disability insurance or long-term-care insurance. In 2008, Congress passed the Genetic Information Nondiscrimination Act (GINA), which prohibits health insurers or employers from genetic discrimination. But neither that law nor the Affordable Health Care Act that came after it applies to other kinds of insurance. “I have a patient who is at 50% risk of a certain disease, but he does not want the test because he fears being unable to get disability insurance,” says Evans.

As sequencing moves toward the mainstream, GINA may need to be broadened to include other types of insurance. That won’t be easy. Congresswoman Louise Slaughter, an 83-year-old microbiologist from New York who sponsored the legislation, describes how opposition from insurance companies led her to focus on protecting people’s jobs and their health insurance instead of casting a wider net. “One of the most important things in the bill is that you can’t be denied coverage for pre-existing conditions,” says Slaughter, whose office has been discussing whether it’s time to start making noise about expanding GINA. “There’s nothing more pre-existing than genes.”

Meanwhile, experts are looking for ways WGS can make health care more efficient. “Most of the people who talk about cost implications talk about how much it costs to do the test,” says Dr. Katrina Armstrong, a professor at the University of Pennsylvania’s Perelman School of Medicine. “But an enormous amount of how this will impact health care is how it will influence who should get other expensive treatments.” In an essay published in the Journal of the American Medical Association in March, Armstrong noted that tests of 21 genes could identify which breast-cancer patients were unlikely to benefit from a particular chemotherapy — knowledge that could save the health care system $400 million each year. “If genomics can help us understand who will get the most benefit and who will get little or no benefit from an intervention, it will take us a long way towards improving patient outcomes and saving money,” says Armstrong.

Another area in which WGS might end up saving money is in assessing the 50,000 babies born in the U.S. each year with hard-to-diagnose disorders. It often takes three to five years to determine what’s causing the baffling symptoms in these children — children like Maya Nieder.

Maya’s mom turned to the Rare Genomics Institute (RGI) — essentially Kickstarter for mystery illnesses — which helped her raise money online to sequence Maya’s exome, the sliver of her genome that contains the genes that do most of her cells’ work. Six hours after a fundraising profile was posted with a photo of Maya and a description of the “silly, cuddly girl” who “loves to read books, paint and play with her dog,” a combination of friends, relatives and strangers had raised the $2,500 needed — a subsidized rate Yale had agreed to charge RGI families.

In June, researchers determined that Maya appears to have a unique mutation; no other person in the world has been reported to have it. For her mother, who was six months pregnant when she got Maya’s sequencing results, finding out that neither she nor her husband had passed a defective gene to their daughter was a relief. It boded well for Maya’s brother, who arrived at the end of September and is acting as all newborns do: hungry and sleepy.

Researchers are now doing more work to confirm that they’ve zeroed in on the gene responsible for Maya’s developmental delays. Assuming they’re right, finding an answer is oddly bittersweet for the Nieders. Maya’s doctors think they know which gene is misfiring, but they have yet to find an effective treatment for it.

Still, it’s hard to place a price tag on the emotional benefits of knowing what’s wrong. For that, Dana Nieder is grateful to the Internet — to the strangers who donated $10 and the relatives who helped fund Maya’s sequencing. “When I talk to the insurance company now, I’m not just a mom saying she has global delays. When we go to see a new doctor, it means I don’t have to say she has this genetic thing but we don’t know what it is,” says Nieder. “There is some sort of security in having something to point to and say, This is it.”

This is the final chapter in a five-part series exploring the promise and pitfalls of sequencing children’s genomes.Read the full series.